The Stovebolt Site Forums The Shop Area Engine Shop update on gas mileage

I talked to the guy at Langdon's Stovebolt. He pointed out the shortcomings of the Rochester carbs, multi-source for parts and no standard parts, parts bought from many suppliers and poor quality control. Now I have to decide what to do next. He also said that the initial timing could be off. He said if it works by sucking on the hose the vacuum advance is ok.

So, he said the same thing ALL of us have been saying for months and in the case of the Rochester’s for years. Go figure.

I am stubborn. But, if you mess with one thing and then there is a cause and effect. I have used those carbs for the last 10 years with no issues but then when the distributor is messed with my gas mileage drops off. What else can I think? When I suggested replacing them he said it was not necessary they should work fine. Btw he sells them also.

The whole idea of using two of the carburetors that are sufficient to run an engine as a single defies logic. Insisting that "they work fine" that way doesn't wash. The laws of physics aren't "suggestions". There HAS to be a downside to over-carbureting an engine, even if the proponents of doing it refuse to admit it. If you're convinced you're going to break out in a terminal case of the hives if you don't have two carburetors on your engine, at least use some common sense and size them appropriately. The Jeep YF I mentioned before would be a very good starting point, as it's designed for an engine small enough that using two of them on a 235 won't create all the venturi velocity and lean mixture problems that running massively too big carbs can and will create. Of course, where dual carb enthusiasts are concerned, logic and reason has no place in the discussion.
Jerry

Ok, Jerry, why after all these years and miles I am experiencing problems that some attribute to the carbs? I am thinking the reason for the 2 carbs that help with the fact I am driving at 65 & 70 mph instead at 45-50. Remind me again what carbs do you suggest.
mshaw230 Offline
Active BB Member

Registered: 12/18/14
Posts: 307
Loc: Washington State
I talked to Tom Langdon, who shed some light on this. The distributor is from a 1985 Chevy S10 pickup. I gave Tom all my information on the car, except that I once again gave the wrong CAM, shucks. That led to the discussion again of the CAM being too big. I really have the Compcams 260H installed, which should be much better for what I want.

Tom said I should start with a much higher timing, 18. When I told him I was around 7 or 8, he said in a very funny way to add another 10. I believe he said I wasn't even on first base and to add 10 and and call him in a week. Of course, he said to run high octane with this advanced. I'm going to run an experiment now, I think, see if it knocks and if it runs better.

Tom said that the distributor curve would help a few %, but a smaller CAM would make a huge difference. I'll call him in a week and let him know how it goes and that I actually had the smaller CAM and see what he suggests.

mdonahue05, that's a great suggestion. I've heard about people who have the machinery to set up distributors. If it's really that I can just start with a higher timing to start with, I'll go that route.
_________________________

beautiful sight.. Plymouth flathead six. I went out to my other garage and found my old intake manifold, still have options.

The nice thing about beating one's head against a brick wall is that it feels so good when you stop. Good luck- - - -you're going to need it!
Jerry

How many experiments did Edison make before he got the light bulb to work?

The picture of the Plymouth engine showed the only carburetor Carter built that was actually worse than the Rochester B!

These things were so bad that Carter actually produced a trouble-shooting chart to send to the dealers. Was never necessary on other Carter carbs:

http://www.thecarburetorshop.com/Service_Carter_BB_downdraft_issues.pdf

Long story about when Plymouth used a Chevrolet W-1 for a few months in 1947, and then had all the complaints (why do cars with the Chevy carb run 5 MPH faster and get much better fuel mileage than the ones with the Plymouth carburetor when the Chevy carburetor is a smaller carburetor???). I think I have posted this before.

Jon.

If you really want to check the distributor, send it to me, I will spin it up on my machine and set it how you want. I don't like the idea of setting the initial timing at 16* or 18*, you should have 5-8 initial and the rest in mechanical advance, then add a vacuum on top of that. You should also try and have all the mechanical in by 2500 or so, so when on the highway at cruising speeds you are at maximum timing. This should give the best fuel mileage.

Go buy you a heavy duty push / pull cable and mount it under the dash. Hook the other end up to the distributor with some sort of temporary pull arm so when you pull the cable knob out, the distributor advances. Leave the hold bolt just loose enough for the cable to work. Get out on the highway and start advancing the timing to you feel it's not helping then back off and see how it runs for a while. This will save countless test drives while closing in on optional timing locations.

You should never have to run premium fuel with the compression you have, it's costly and any fuel mileage gains will be offset by the price of the fuel. My 8.0-1 compression 250 will run on 87 octane with as much timing as want, I believe it set for 38* total, could be higher, I haven't checked it for years.

This an HEI, no external movement. But thanks for the offer.

You have finally found someone who is willing to tell you what you want to hear. Be sure to pay him well while he's tinkering with stuff that will do absolutely no good.
Jerry

PLEASE report back on the test with the distributor at 18 degrees static advance. Would guess the engine will be difficult to start, will gain power in the lower RPM's, LOSE power in the upper RPM's, and overheat at cruise.

Looking forward to your report.

And premium fuel??? I don't need premium for my 390 with 10 1/4 compression unless I am pulling the 18 foot trailer loaded. Never for normal driving.

Jon.

Jon, I don't know where it will be set. I put one tank of mid-grade as an experiment. No difference. I thought it would make some difference in the timing set but it still pinged a little. It will be a few days until something else gets done I am having a medical procedure done on Tuesday. I still in the belief that the Hei is at fault because it was the one thing that was messed with before the mileage dropped off. If I don't get it sorted out I am still doing better than a lot of people with 235 engines. Jon, I looked at your truck, nice job, I will have to look at my brother in law's Corvair carbs, he stores it with me in the winter. Jerry, as far as paying, they do a lot of things and don't charge me because they did most of the work on it from the beginning of the transformation and they really like the truck.

Good luck with the medical procedure!

Jon.

And stay away from the Corvair carbs, they are a pain to tune. There is no enrichment circuit, so you get one setting, rich or lean, not really a middle. I ran three of them for a few years, I could get decent mileage with no power, or good power with no mileage. I still have the three of them set on a manifold ready to install ( 250 ci ) and a bunch extra parts.

Same here, Ron...good luck with the medical procedure.

Carbking, being technologically challenged I should have said 18" of vacuum. I was trying to write down his advice and hold a cell phone so I am sure I missed a lot of what he said. He was very accommodating since I purchased the Hei from him 10 years ago and he could me have sold me some unneeded parts. He even gave a cross-reference number for the vacuum advance that could be bought locally or from Amazon. BTW he sells the part.

MUCH more understandable than 18 degrees advance. Vacuum tests at different engine loads, along with compression and leak-down tests, are very good indicators of where to look for issues.

Again, good luck on your medical procedure, the truck will wait.

Jon.

There's nothing wrong with dialing in a few more degrees of initial timing advance- - - - -as long as a corresponding amount of centrifugal advance is reduced. For instance, let's start with a distributor for an engine that is supposed to be run with an initial timing of 8 crankshaft degrees before top dead center. That one's probably going to have a centrifugal advance of around 25-27 degrees, and another 10 degrees of vacuum advance, resulting in around 45 degrees of total spark advance at light throttle cruise. As soon as even a slight amount of throttle is applied, the vacuum goes away- - - -leaving around 35 degrees of advance during acceleration. A more radical cam can benefit from added initial advance, so let's dial in an extra 5 degrees of initial, and restrict the travel of the centrifugal advance weights by the same amount. Total timing doesn't change, nor does the advance available during acceleration (IMPORTANT for preventing detonation!)- - - -we've just altered the advance curve a little.

Very few professional mechanics, and virtually no hobbyists have even a basic understanding of how a timing advance curve is calculated. It's a mix of engine speed, load, manifold vacuum, and a considerable amount of "cut and try" using either a dyno or a test drive course so adjustments can be evaluated under identical operating conditions. Wild guesses and anecdotal information just doesn't count!
Jerry

High speed enrichment circuits showed up in latter model Corvair Carbs starting in 1965.

I wish I understood even a little part of that Jerry but thanks. I do appreciate your input, wish you were closer to sort this all out.

A road trip isn't an impossibility- - - -what's Indiana's policy on a Tennessee citizen being able to defend himself? I don't go anywhere my pocket rocket is unwelcome if I can possibly avoid it!

Hmmmm- - - - -430 miles, according to MapQuest- - - - -a little over half the distance to John 's place in Maryland, and I manage to get there occasionally!
Jerry

Jerry - I am one of the ones that knows not a lot about distributor curves. And at my age, I don't need to learn

If I needed a distributor recurved, I would find someone that DOES know.

However, to date, I have never felt the need for a recurve. Even on my 450 HP 390. I found a 390-GT 1967 (pre-smog) distributor, and used it in its stock form. I have found GENERALLY the engineers knew what they were doing, especially for street vehicles.

The only race car I ever built had a factory racing distributor available, which is exactly what I used. And not ashamed to admit the car was faster than the driver! Interestingly, at least to me, the factory carburetion was two 500 CFM 2-barrel carbs on a 121 CID 4-banger. It ran pretty good.

Ron has corrected the 18 degrees of advance to 18 inches of mercury. My comments about the 18 degrees of advance (on the street) were figuring he would need to recurve to final advance, PLUS he would need a good starter and a large battery.

Jon.

Didn’t know you made house calls, Dr. Jerry. I have a long list of items that need sorted out.

I’m fairly certain your means of defense are more than welcome in Missouri.

Iffn you do a house call to JW51, I am close to being on the way (depending on how you come from TN).

Promise to show you carburetors even you have never seen

Jon.

Sounds to me like we should be the ones doing the road tripping. We could all just pop in at Hotrod's compound. I envision slow rolling hillsides covered in tents of avid truck enthusiasts gathering to work on old trucks... Oh wait, that is called Homecoming.
Maybe we need to start a Middle-of-the-country version of Homecoming.

I host 50-something firearm enthusiasts from the Guns & Ammo website every Memorial Day weekend, and the crowd starts gathering about the Wednesday or Thursday beforehand, and some of 'em don't leave until Tuesday. That's been going on for around 15 years. If my long-suffering wife saw a bunch of truck nuts converging on our place, there would probably be a wake and a funeral to attend! She and several of the wives/girlfriends/significant others who attend that event put on a Saturday lunch during the shoot that rivals the target shooting for popularity! We've had visitors from as far away as Canada and New Zealand at times!
Jerry

Just hop skip and jump for me, I would go.

OK, just so this isn't a total thread hijack, I do understand re-curving a distributor, my efforts usually only involved going to lighter springs or grinding the wights a bit. My old 340 Duster came stock with a dual point distributor and was a mystery to most, but the point (pun intended) was to increase the dwell angle. This allowed the coil more time to produce more voltage to fire the stock Champion N9Y plugs (also stock for the Hemi's).

But, Jerry Jerry Jerry...you just hit on one of my other passions that I know more about than the average Joe, but also know so little. It's kinda like my knowledge of all things automotive. Shooting. While in ND for a few years I spent considerable time tuning & shooting a lit’l .223 Savage Axis I won with $20 of raffle tickets at the VFW. New trigger, lots of stock work and it was good for sub MOA @ 300 yds.

Then I became friends with a K-Class shooter and he showed me what shooting was about.

Wish I had a suitable long gun and knowledge to shoot at your place, perhaps next life.

On the dual carbs and fuel mileage, in the early days here there were several guys running dual Rochester B carbs on 235's and reporting better fuel mileage. two names I remember is Cosmo and Barry Weeks.There were a few others ,the guy with the 261 in a 37 truck.They don't use this site any longer but Tim Lederman is still here and might remember the actual stories.The fuel distribution of a single carb on a long log intake is terrible. GM actually tested it found the center cylinders are over rich, end cylinders lean.Two carbs can give better fuel/distribution and increase efficiency...........Some stuff sounds unlikely but unless you have actually tried it, it not always fair to say it can't be.....

Fast, what were you doing in 1962? That's when a friend of mine back in high school put a 3-carb manifold on a 216, and then adapted three Stromberg 97 2-barrels to it. A week and four engine fires later, he was back to a single carb. Some of us with more than a passing amount of experience are willing to share half a century of our real-world knowledge, but we're ridiculed for doing it. Yes, there are ways to make multiple carbs work. Sometimes, though rarely, they actually perform better and/or get better gas mileage, but the smart way to bet would be on the opposite result. I know how to make a 3-carb setup on an inline six do that, and I've got a project in mind that will have that type of fuel system. It definitely won't have three or four times more carburetor than the engine can handle, however. I'm stubborn, not stupid!
Jerry

Hot Rod Lincoln, we have gone from two Rochester B's on 235-261's by adults with some tuning experience in my story to 3 97's on a 216 done by a high school youth....Sorry, no comparison... Oh , I was 15 in 1962 and the hot cars in school were V-8's...

I hate to jump back in and stir more controversy but all I will say, the 2 carbs worked for 9 years just fine then after the distributor adjustment my mpg dropped by 25%. Btw I had the timing set to specs, today.

I am beginning to wonder if, rather than your MPG dropping by 25%, that instead your math skills have improved by that same 25%. Either that or your odometer was way off when you were seeing these improbable MPG numbers. The likelihood of an AD with the wind resistance of a 5'X 7' brick wall getting 20 MPG at 70 MPH (or even 60 MPH) defies the law of physics, regardless of engine, number of carburetors, gear ratio of transmission and rear end. I may be all wet. I am just spitballing here.
Carl

A thought, why all of a sudden did my math improve?? It is not my strong suit but adequate for surviving 55 years in retail sale as a salesman and manager. I have gone over the figures for the last 10 years checked and rechecked. If you forget about the mileage and fuel used, what about the time frame between fill up. 2 hrs now around 3 before and highway speed, around town I literally watch the gauge dropped. The mystery continues at least for me. Also, it has provided a long narrative.

Figured it out for you:

Gas milage trick